1. Field of the Invention
This invention relates generally to an apparatus for transferring heat to and from fluids and more particularly to heat transfer apparatus for use in transportable liquid containers such as railroad tank cars and tanker trucks.
2. Description of the Prior Art
Fluid containers, and in particular, large volume tanks are extensively used for transporting fluids in commerce. The most common of these containers are railroad tank cars and tanker trucks. These containers are frequently the most economical for shipping large quantities of materials amenable to flowable loading and unloading.
In many cases it is desirable to transfer heat either to or from the fluids contained in the tank. This may be necessary to heat a material to reduce the viscosity such that it will flow easily or to cool the material down to avoid dangerous situations or to facilitate handling.
One type of material frequently shipped in transportable fluid containers, and particularly in railroad tank cars, is elemental sulfur. One manner utilized for transporting sulfur is to heat it above its melting temperature and to pump it into tanker cars while in liquid form. It is then transported to its destination in the tanker cars. During the transportation, the sulfur will cool to below its melting temperature and, at least partially, solidify. Therefore, it is necessary to reheat and remelt the sulfur prior to unloading. Various apparatus have been utilized to remelt solidified sulfur in railroad tanker cars.
One method of heating sulfur contained in tanker cars which has been previously utilized is to arrange a series of ordinary pipes in a tanker car and to pump either heated steam or a heated conductive liquid through the pipes, thus transferring heat to the sulfur in the tanker car. However, this method has been substantially abandoned in recent years due to inefficiency of heating and substantial breakage in the pipes. Railroad cars are frequently subjected to significant inertial shocks during coupling transactions and at other times during use. Thus, the interior pipes, which were welded to the structure of the tanker car, were frequently damaged by the shock. The considerable down time caused by pipe breakage and other damage to the heat transfer system were a major disadvantage.
The method most commonly utilized presently to heat solidified sulfur in railroad tank cars is a series of heating pipes arrayed around the outside of the tanker car itself. These pipes are welded directly to the exterior surface of the tank material. Conductive heat transfer thus takes place between the contents of the pipe, through the pipe wall, through the weld and finally through the tank wall to the contents.
The exterior welded pipe apparatus has significant disadvantages in that a great deal of the heat is dissipated into the environment since only a small portion of the pipe is actually in contact with the tank material. Furthermore, the tank material itself dissipates and radiates outward some of the heat transferred to it. This exterior welded structure has a further disadvantage in that it is difficult to construct because a great deal of welding must be done between the pipes and the tank wall. This results in a large amount of assembly line time being spent on the installation of the exterior pipes. Furthermore, although the pipes are welded to the exterior of the tank, the pipes retain some independent inertia and are subject to some breakage due to the shocks involved in coupling the cars.
None of the prior art apparatus for heat transfer in railroad tank cars have solved the problems of eliminating breakage and stress while maximizing the transfer of heat to the contents. These same problems are present and remain unsolved in other mobile liquid containers, as well.